A concrete mixer truck having a mixer drum capable of carrying freshly mixed concrete is used conventionally. The freshly mixed concrete is generated by introducing cement, aggregate, water, and so on into the mixer drum of the concrete mixer truck and driving the mixer drum to rotate so that the materials are mixed.
JP2005-022640A proposes a concrete mixer truck that includes an inspection instrument for performing a quality inspection when transported freshly mixed concrete is unloaded. In this concrete mixer truck, a slump test for measuring a fluidity of the freshly mixed concrete is performed on the freshly mixed concrete as the quality inspection. In a slump test, a slump, which is a numerical value indicating the fluidity of freshly mixed concrete, is measured. The fluidity of the freshly mixed concrete increases as the measured slump increases.